The present invention relates to an interactive service utilizing digital transmission by a Cable TV (CATV).
In a conventional Cable TV, a pay service called Pay Channel is offered. This requires an agreement for a desired channel in advance, and a subscriber requests an operator at a center to subscribe for a pay program channel in advance by a telephone call or a request form. The operator receiving the request registers the pay program channel in a host computer for administering subscribers in accordance with the request and thereby activates a micro computer at a terminal of the subscriber's side based on the registered data. The Pay Channel is devised so that, when it is permitted to receive the requested pay channel through this procedure, operation of a descramble portion shall be possible, that is, scramble of signals are released to make viewing of the pay program channel possible.
There is also a system called Pay Par View (PPV). This is not an agreement per pay program channel but a mode for purchasing per program that a subscriber desires to view. It is common to give a program number for each program to control a pay program in the PPV.
Since a certain subscriber purchases a program at a specific time in order to correspond to the PPV, an exclusive use channel is required for delivering a program to the subscriber. Although a conventional Cable TV station conducting analog transmission has the capacity to transmit television channels almost 60 in number, the reality is that about 30 channels, only a half of the total number, is utilized in the actual service. These 30 channels consist of programs such as programs for program suppliers transmitted by ground television broadcasting and broadcasting and communication satellites and programs planned and produced by cable television operators independently. Community programs or the like in close contact with communities such as cities, towns and villages are included in the independently produced programs.
As described above, although a Cable TV has the capacity of transmitting 60 channels, same bands are in fact secured for television broadcasting electric waves and some channels cannot be actually used due to distortion of electric waves or the like generated from equipment. Therefore, the reality is that about 40 channels are actually available for use and the number of channels to be assigned to individual subscribers for delivering pay programs as PPV by a Cable TV center is limited to only a few.
Incidentally, the analog transmission of the conventional technology could transmit only one program channel for a 6 MHZ cable band. However, it has become possible to transmit, using one analog channel band, about a few channels of animation image signals (MPEG2) digitally compressed by transmitting digital signals inside cables due to the recent progress of technology.
Further, the conventional Cable TV line uses coaxial cable lines up to 450 MHZ, but transmission lines called a city type Cable TV using optical fiber together with coaxial lines has become common.
In the transmission lines, a highway system is laid with transmission lines of optical fiber to the vicinity of a subscriber's home from a Cable TV center and the last distance of about 1 km is connected with coaxial cable lines. Recently, most of the regions planning to transmit from a center by optical fiber utilize the city type Cable TV. The city type Cable TV simultaneously functions as transmission lines for interactive communication as well and is discussed to be used as an interactive type Cable TV system.
With such background as described above, digitalization of AV (Audio Visual) and networking have advanced rapidly and digital technology based on computer technology is spotlighted as represented by the Information Super-Highway Plan in the United States of America, a country advanced in a Cable TV.
In an interactive service by such a Cable TV, it is common to be rendered such limitation as QAM output channel limitation arising from the number of QAM modulator being a center facility and limitation arising from available frequency channels, starting with output stream number limitation of a video server. Incidentally, QAM (Quadrature Amplitude Modulation) is one of digital modulation methods with increased frequency utilization efficiency.
Although frequency utilization efficiency is increased, simultaneous delivery is only possible to subscribers equivalent to the number of bands (6 MHZ band channel) X multiple channels.
On the other hand, a subscriber wishes to have desired programs delivered at the time he or she wants to watch them. However, if lines for all the subscribers are to be secured, it will lead not only to the increase of facility expenses at a center's side but also to problems deriving from limited space for setting center facilities.
The present invention has been devised in view of the problems and it is the technical subject to provide technology utilizing equipment set in a center's side by restraining the number of digital lines to subscribers to a predetermined number while maintaining on-demand services to subscribers.